In making Transmit/Receive (“T/R”) chips, one limitation frequently encountered is the same transistor may not be optimal for both transmit and receive functions. For optimal transmission applications, higher output power is desired. Such a characteristic may be provided by a power amplifier utilizing “field-plate” devices with high breakdown voltage. For optimal receiver applications, on the other hand, high dynamic range, low noise figure, and high RF survivability may be desired. Such characteristics may be provided by low-noise amplifiers utilizing high-frequency “T-gate” devices.
GaN HEMTs are good candidates for applications in high-power, solid-state, mm-wave power amplifiers because of the high electron velocity and high breakdown voltage of the material. GaN is also promising for robust receiver applications which require high dynamic range, low noise figure, and high RF survivability.
However, integration of T-gate and field-plate devices has not been demonstrated previously for GaN wafers due to the relative immaturity of GaN technology compared to other material systems, combined with inherent processing challenges. Furthermore, the use of traditional gate fabrication processing techniques to integrate T-gate and field-plate devices is not straightforward since it will require two separate lithography and metal evaporation processes, which can lead to reduced yield.
While components can be fabricated on separate wafers and then assembled in a hybrid module in which a power amplifier on a “field-plate” is fabricated on one wafer and an LNA on a separate “T-gate” wafer, such a hybrid module may be substantially larger than a single-chip approach, integrating separate chips requires additional design & assembly at module level and there may be some insertion loss at each transition (e.g. wire-bonds) between the separate chips and the hybrid components.